Multi-trace element distribution in olivine from the Eastern Deeps deposit, Voisey’s Bay Intrusion, Labrador: olivine composition as a record of ore-forming processes in evolved magma systems

The distribution of Ni-Mg-Fe in olivine is used extensively to characterize mafic intrusions, and, in combination with other geochemical tools, assess their Ni-Cu-Co sulfide mineralization potential. Despite the availability of sensitive analytical techniques (e.g., Secondary Ion Mass Spectrometry – SIMS) and the proven importance of olivine multi-trace element studies to igneous petrology, a more comprehensive geochemical approach of determining multiple trace elements in olivine has never been adopted for economic geology applications. For this dissertation I implemented a refined SIMS analytical protocol for the determination of multiple major-trace elements in olivine from the Eastern Deeps Intrusion (EDI), a part of the Voisey’s Bay Intrusion (VBI), Labrador. The study demonstrated that systematic, lithology-dependent trace element variations in olivine, particularly in Ni, Co, Cr, Mn, and Zn, characterize critical ore-forming processes and indicate the proximity to zones of massive sulfide mineralization in the EDI. SIMS is an analytical technique for the in-situ, micrometer-scale determination of elements in a solid sample with very low detection limits. Chapter 2 introduces the SIMS analytical parameters applied for the olivine analyses and further discusses the reference material development and the sequential empirical calibration. The subsequent chapters detail the SIMS studies of olivine from the EDI and Pants Lake Intrusion (PLI). Chapter 3 demonstrates that lithostratigraphic variations in olivine Ni-Co contents (~80–2,500 ppm Ni; ~170–370 ppm Co) in the EDI indicate magmatic episodicity and multiple sulfide saturation events. The basal, incongruent olivine Mn-Zn enrichment (up to 12,000 ppm Mn; up to 680 ppm Zn) reflects country rock contamination followed by a diffusive trace element exchange with surrounding sulfide liquid. Chapter 4 discusses the application of the olivine trace chemistry as a lateral vector towards sulfide mineralization in the EDI, and as a fertility indicator for mafic intrusions on a regional scale (ex. PLI). Progressively increasing contents of Mn-Zn in olivine towards the inner basal margin of the EDI indicate spatial (vertical and lateral) proximity (~150m) to massive sulfides. A strong compositional bimodality (e.g., Ni-enriched and Ni-depleted) of olivine also increases the potential for inherent economic mineralization (ex. VBI). This study considerably improved our understanding of systematic compositional variations in olivine as a response to essential ore-forming processes in mineralized mafic magmatic systems

Episodic hydrothermal alteration recorded by microscale oxygen isotope analysis of white mica in the Larderello-Travale Geothermal Field, Italy

Microscale oxygen isotope analysis (18O/16O) of minerals can identify distinct events of fluid-rock interaction. This method is, however, still limited to a few major and accessory minerals of which most are anhydrous minerals. We present the systematic study of oxygen isotope distribution in white mica by Secondary Ion Mass Spectrometry (SIMS). Texturally and chemically distinct white mica populations in granitic and contact metamorphic rocks from the Larderello-Travale geothermal field (LTGF), Italy, record stages of magmatic crystallization, metamorphic-hydrothermal replacement and fluid-rock interaction. The large range in intra- and inter-grain white mica δ18O values between 1–14 ‰ reflects varying protoliths and degrees of fluid-mineral interaction at variable temperatures (180–450 °C present-day temperatures; p.d.T.). This variability reflects the large-scale circulation of both (1) magmatic, syn-intrusive to early contact metamorphic hydrothermal fluids with high-δ18O values, and (2) meteoric fluids with δ18O values of –7 ‰ during a post-intrusive, late hydrothermal stage. Metasedimentary rocks from the upper reservoir contain distinct white mica populations occurring in close proximity (μm-scale), including detrital grains (δ18O = 12–14 ‰; high Na, low Mg), partially altered white mica (δ18O = 8–9 ‰) and late hydrothermal white mica (1–6 ‰; low Na, mid Mg). The late hydrothermal white mica has similar δ18O values to other secondary minerals and is in equilibrium with meteoric-dominated fluids with a δ18O of –6 to 0.5 ‰, which circulated in the late hydrothermal stage. Downhole towards the lower reservoir, white mica from two contact metamorphic micaschist samples shows either (1) homogeneous δ18O values of ca. 9 ‰ likely due to recrystallization in the contact metamorphic hydrothermal stage (T ca. 600 °C), or (2) a large spread in δ18O from 2 to 12 ‰ within and across grains of variable texture and chemistry in the host rock and a cross-cutting quartz-white mica vein (ca. 300 °C, present day temperature; hereafter p.d.T.). This contrasting δ18O signature of white mica is also recorded in granite cored at up to 4.6 km depth. The Carboli granite contains white mica with a homogeneous magmatic δ18O of 10 ± 0.6 ‰, whereas older granite samples from Radicondoli have magmatic to hydrothermal white micas that vary in δ18O from 4–10 ‰. A pronounced intra-grain δ18O variability of up to 6 ‰ occurs in white mica domains with higher Fe-Mg-Ti halos around inclusions of chloritized biotite, as a result of interaction with dominantly meteoric fluids that infiltrated to depths of at least 4.6 km. In the Porto Azzurro granite on Elba, Italy, altered white mica has δ18O values of 2.6 ‰ down from 10 ‰ in unaltered grains. The distribution of oxygen isotope ratios in white mica is thus firstly a result of pervasive versus selective fluid alteration (at depth, sample and grain scale). Secondly, the actual preservation of these μm-scale variabilities indicates that volume diffusion is not detectable at microscale at p.d.T at or below 350 °C where most of the heterogeneous white mica is found. Selective, sample- and grain-scale fluid penetration occurs episodically and anisotropically, on micro- and megascale, along faults, fractures and cleavages, producing lower δ18O white mica at various times in zones of higher secondary permeability and active hydrothermal fluid circulation

O-Hf isotope constraints on the origin of zircons in high-pressure mélange blocks and associated matrix rocks from Tinos and Syros, Greece

Most previously dated zircons in high-pressure mélange blocks and associated matrix rocks from Tinos and Syros (Cyclades), Greece, yielded ion microprobe (SHRIMP II) U-Pb ages of ca 80 Ma. In many cases it remains unclear whether the zircons are igneou

Rare predicted loss-of-function variants of type I IFN immunity genes are associated with life-threatening COVID-19

BackgroundWe previously reported that impaired type I IFN activity, due to inborn errors of TLR3- and TLR7-dependent type I interferon (IFN) immunity or to autoantibodies against type I IFN, account for 15-20% of cases of life-threatening COVID-19 in unvaccinated patients. Therefore, the determinants of life-threatening COVID-19 remain to be identified in similar to 80% of cases.MethodsWe report here a genome-wide rare variant burden association analysis in 3269 unvaccinated patients with life-threatening COVID-19, and 1373 unvaccinated SARS-CoV-2-infected individuals without pneumonia. Among the 928 patients tested for autoantibodies against type I IFN, a quarter (234) were positive and were excluded.ResultsNo gene reached genome-wide significance. Under a recessive model, the most significant gene with at-risk variants was TLR7, with an OR of 27.68 (95%CI 1.5-528.7, P=1.1x10(-4)) for biochemically loss-of-function (bLOF) variants. We replicated the enrichment in rare predicted LOF (pLOF) variants at 13 influenza susceptibility loci involved in TLR3-dependent type I IFN immunity (OR=3.70[95%CI 1.3-8.2], P=2.1x10(-4)). This enrichment was further strengthened by (1) adding the recently reported TYK2 and TLR7 COVID-19 loci, particularly under a recessive model (OR=19.65[95%CI 2.1-2635.4], P=3.4x10(-3)), and (2) considering as pLOF branchpoint variants with potentially strong impacts on splicing among the 15 loci (OR=4.40[9%CI 2.3-8.4], P=7.7x10(-8)). Finally, the patients with pLOF/bLOF variants at these 15 loci were significantly younger (mean age [SD]=43.3 [20.3] years) than the other patients (56.0 [17.3] years; P=1.68x10(-5)).ConclusionsRare variants of TLR3- and TLR7-dependent type I IFN immunity genes can underlie life-threatening COVID-19, particularly with recessive inheritance, in patients under 60 years old